That is what this paragraph was trying to explain:
If you are having problems with other software reading information written by ExifTool, if possible try first writing the information from the other software, then use ExifTool (with the -a and -G1 options) to determine where the information was written. Once you know where it should go, you can use ExifTool to write to this location. You can read or write information in a specific location by prefixing the tag name on the command line with the desired group name. ie) "-ExifIFD:DateTimeOriginal"
- Phil